Polyurethane magnetic coating composition

ABSTRACT

A POLYURETHANE MAGNETIC COATING COMPOSITION FOR RECORDING TAPE COMPRISING A MAGNETIC PIGMENT IN A THERMOSETTING BINDER MADE FROM A LOW MOLECULAR WEIGHT DIOL, A HIGH MOLECULAR WEIGHT POLYESTER DIOL HAVING A MOLECULAR WEIGHT BETWEEN 10,000 AND 30,000 AND A TRIISOCYANATE.

United States Patent 3,574,684 POLYURETHANE MAGNETIC COATING COMPOSITION Louis M. Higashi, San Jose, Calif., assiguor to Memorex Corporation, Santa Clara, Calif.

No Drawing. Filed May 26, 1965, Ser. No. 459,074 The portion of the term of the patent subsequent to Nov. 19, 1985, has been disclaimed Int. Cl. H01f /02 US. Cl. 117-237 4 Claims 7 ABSTRACT OF THE DISCLOSURE A polyurethane magnetic coating composition for recording tape comprising a magnetic pigment in a thermosetting binder made from a low molecular weight diol, a high molecular weight polyester diol having a molecular weight between 10,000 and 30,000 and a triisocyanate.

This invention relates to magnetic recording media and more particularly to a magnetic recording media and method of producing the same in which a magnetic pigment is dispersed and supported in a reactive polyurethane binder system.

Magnetic recording media are generally formed by dispersing magnetically susceptible particles such as Bamma ferric oxide which has a spinelle lattice structure in a suitable polymeric binder solution, and coating this dispersion upon a flexible substrate such as paper, cellophane, films of polyvinylchloride, polyethylene or polyester film or rigid substrates such as glass, metal or plastic plates.

With the development of more precise and higher speed magnetic recording and playback equipment, it has become a common object in the art to produce more durable coatings that have less tendency to shed binder and magnetic particles. Such coatings are known by those skilled in the art to maintain optimum signal output over longer periods of operation and are known to have less tendency to develop signal dropouts which are localized signal loss areas on the surface of magnetic tape.

A further object of this art is the development of magnetic coatings which possess the necessary flexibility without the incorporation of plasticizers and elastomers. The presence of such agents was often found to create problems of incompatibilities in the binder system as well as lead to blocking tendencies of the coating in environments of higher relative humidities and storage temperatures. Blocking is the tendency of the coating to adhere to the back of the flexible substrate When magnetic tape is stored under tension under adverse environmental conditions.

In accordance with this invention, a novel magnetic recording media is produced in which a magnetic pigment is dispersed in a polyurethane binder system where the polyurethane binder system is reacted after dispersing the magnetic pigment therein. The practice of this invention leads to a durable magnetic recording media of low debris formation, improved abrasion resistance, and storage sta bility under adverse environmental conditions.

The reactive polyurethane binder system employed in accordance with this invention is a reactive mixture of a low molecular weight diol, a high molecular weight diol, and a triisocyanate. The low molecular weight diol forms from about 10 to 90 weight percent of the mixture of the two diols with the lower percentages being employed for the lower molecular weight diols, and the amount of triisocyanate is selected to give a ratio of isocyanate groups to hydroxyl groups in the mixture which is Within the range of 0.8 to 1.5, and preferably about 1.25.

3,574,684 Patented Apr. 13, 1971 The low molecular weight diol may be a primary or secondary aliphatic glycol containing 2 to 22 carbon atoms, a polyether glycol containing 4 to 22 carbon atoms or a polyester diol having a hydroxyl number of 10 to 100 and having the following general structure:

where R is the carbon chain of a glycol represented by and R is an aliphatic hydrocarbon radical containing about 6 to 16 carbon atoms, and n is an integer having a value such that the molecular weight of the low molecular weight polyester diol is 216 to 3240.

The high molecular weight diol may be a polyester having a hydroxyl number of 1 to 40 and having the following general formula:

where R is a benzene ring, in the ortho, meta, or para configuration, R is an aliphatic hydrocarbon radical containing about 6-16 carbon atoms, x is an integer from 7 to 30, and n is an integer having a value such that the molecular weight of the high molecular weight polyester is approximately 10,000 to 30,000.

The triisocyanate may be triphenyl methane triisocyanate, or a prepolymer having the general formula:

where R is a divalent benzene radical containing an aliphatic hydrocarbon side chain of 0 to 18 carbon atoms.

In accordance with the method of this invention, a mixture is prepared containing the desired amount of magnetic pigment, the desired amount of low molecular weight diol, and the desired amount of the high molecular weight diol, and there may be incorporated into the mixture a solvent which is free of reactive hydroxyl and isocyanate groups. Also there is incorporated into the mixture a catalytic amount of a catalyst such as triethylene diamine, methyl amine, triethanol amine, urea, lead octoate, dibutyltin dilaurate, and metal acetylacetonates.

The mixture of magnetic pigment, low molecular weight diol, and high molecular weight diol containing the catalyst and solvent if desired is mixed to uniformity for instance in a paint ball mill for a period of 10 to 20 hours, and thereafter the triisocyanate is added to the mixture. In this regard, it should be noted that advantages in the shelf life of the mixture after the triisocyanate has been added are obtained where the aromatic group in the triisocyanate (the group R mentioned above in the formula) contains the alkyl side chain of at least one carbon atom as a substituent on the benzene ring adjacent to the reactive isocyanate group. 7

The components of the recording media are preferably employed in the following amounts, the parts given being parts by weight: where the low molecular weight diol is the polyester base diol, 4-10 parts of the low molecular weight diol are employed with 60-85 parts of magnetic powder, 1 0-27 parts of the high molecular weight diol, 1-3 parts of the prepolymer triisocyanate, 5080 parts of keytone solvent, and 0.05 to 1.0 part of triethylene amine, and the low molecular weight diol forms 20 to percent of the combined weight of the low molecular weight diol and high molecular weight diol. Where the low molecular weight glycol or the polyether glycol is employed as the low molecular weight diol, 60 to 80 parts of magnetic powder are employed with 0.7 to 1.9 parts of the low molecular weight glycol, and 10.0 to 26.6 parts of the high molecular weight polyester diol, 9.3 to

and polypropylene glycols yield more flexible, softer coatings which are more elastomeric in nature.

The following is a list of alternate diols sold by Union Carbide Company which may be employed, and similar materials are supplied by various manufacturers and may 1 1.5 parts of the prepolymer triisocyanate 50 80 parts of be freely substituted: keytone and 0.05 to 1.0 part of dibutyltin dilaurate.

The following specific examples are set forth for the t y g y purpose of illustrating the practice of the invention. Many dlfithylene glycol variations and modifications of these examples will be methylene g y l apparent to those skilled in the art and may be made r hylene glycol without departing from the spirit and scope of the in- P Py glycol vention. dipropylene glycol EXAMPLES 1-3 1,3 propane diol In these examples, the magnetic pigment employed was polypropylene glycols spch as Nlax PPG 1025 2025, 3025, 4025, Max LG Nos. 56, 168 moisture free gamma ferric oxlde. The low molecular 2 meth 3 r0 anediol weight polyester diol was Multron R16, made by Mobay y y i p P 2-ethyl-1,3-hexand1ol Chemical Company. ThlS polyester is based on diethylene hex lane 1 col glycol and adipic acid and has a molecular weight of apy g y pf y 2550 alfld a hydroxy1 l of The other diols which may be used include butynediol and h1g h molecular y l P y havlng a molecular butenedlol, a product of Antara Chemical Company and rrt ta aznta 5.32 .2 3.entran 1? 1 5? 51:

0 1 1 1 T 0 to w ic are so y t e e erson ernica the Goodyetlr Chemical p y and is a Prepolymer 9 Company. The following formulations were employed Polyethylene glycol tefephthalate and Sebacate- The for making magnetic recording media, and these media on r and t e wet coatings were cure at or t ree minutes.

consists of an adduct of one mole of trimethylol propane and three moles of toluene-2,4-diisocyanate prepared as a 60% solids solution in a so-so blend of Cellosolve Examples acetate and xylene. Mondur CB60 sold by .Mobay Chemi- 4 5 6 7 cal Company and Tranco 375B sold by Trancoa Chemical I (H t b ht Company are eqliwalents' l/lar ie%ic gigne1 ..l 75.00 75.00 75.00 75.00

The 49000 series of Du Pont polyesters having a hy- PentanediolLIS Til 1 1. 2 2 3.75 5.33 droxyl number of 11 may used l of PE2 07 a i i s s9s y"1i3esfiif??? 5: 00 5: 00 5:00 5: 00 as well as Goodyear Chemlcals V1tel PE100 and Vitel g0% r -g0o re o1 ner 15.20 21.05 10.30 55.66

0 me Q efirsnisrlime 100.00 106.96 93 66 76. 40

W1tco Chemicals Foamrez with a hydroxyl value varilalbtg tg sxnin ies 4-7; 1 25 1 25 1 25 of 52 may be equivalentto Multron R16. 40 Low g 'g 'a ma '2 35i A 20% solution of triphenyl methane triisocyanate in (in percent) 6.3 10. 3. 6.3 monochloro benzene and having 6.8% free isocyanate 7%; 73' 0 78 7% content may be used mstead of P49-60CX. ThlS prepolymer is manufactured and sold by Mobay Chemical Company under the trademark of Modul The tapes prepared in these preceding examples were The follow g m f given in Parts y Weight 0f the 45 subjected to standard magnetic tape tests and in these above ldelitlfied 'na fl W61e employedgorhmaklng the tests were compared to a high quality precision magnetic magnetic y a magnetic p an t e magnetic tape which employs a vinyl binder system made of a media @1118 Produced were pp to a Mylar substrate in non-reactive mixture of a fully reacted polyurethane and conventional manner, and the wet coatings were cured 0 a copolymer f vinylidene Chloride acrylonitnle at for three mmutes- The results of standard magnetic tape tests on the tapes of the preceding examples are reported in the following Exam 1 table. In these tests, taber abrasion measurements are expes pressed as m1ll1grarns of coating lost when the tape was 1 2 3 subjected to the abrasion action of two #CSlO abrasive Ingredients, parts by weight: wheels at 1000 grams pressure for 500 rpm. The blocking 5 315232;255E553:::::::::::::::::::::::: 5:22 3:33 3222 tests were run by Winding threeteet of 1/2 inch Wide Polyester (30% in cyelohexanone) 71.00 56.00 71.00 net1c tape around a inch diameter metal shaft under fi j 15 pounds tension and exposing the wound tape to 160 P49-60CX prepolym 3.97 5. 40 3.97 60 F. and 84% relative humidity for 16 hours and then congg gfi fiigg g zg f g 9M0 9999 ditioning thetape under ambient conditions for 24 hours N00 0H 1. 25 1.25 1.25 prior to unwinding.

Low molecular weight diol/total diol (in 26 5 40 0 26 5 70. 1 70. 1: 7014 0. 77 0.77 0. 77 Test 1 2 3 4 5 0 7 Vinyl Neck down. A A A A A A A A Roll A A A A F A A A EXAMPLES 4J7 011"? Hi Hi HB' F g 21 Hi H1? H In these examples the preparation of the magnetic Taber mg loss 32.0 43.5 30.0 18.5 23.0 36. 48 50 media was repeated in a similar way but employing i 2 1 f: 2 A A g pentanediol 1,5 as the low molecular weight diol. This low Wnnk1 e 1 7116 1 1: 1 A c- A A- 1 molecular weight diol has a hydroxyl number of 1076 and %6L fs fi "'13-" g 5 m is the preferred low molecular weight glycol for use inthis Melting point, C.. 205 205 205 220 220 220 220 150 invention. The lower molecular weight diols yield tough, I Pass100% less flexible magnetic coatings of greater hardness while 2 Pass 50%.

Pass the higher molecular weight diols such as polyethylene The melting point of the polyurethane coatings was 205 C. and above as compared to 150 C. for the vinyl system. Due to this higher melting point such coatings were superior in performance when subject to high frictional heat generated on the surface when used on high speed tape transports. The tapes were tested on a commercial video tape recorder where the tape was held stationary against the high speed revolving helical scanner, and no signal dropouts were observed on the polyurethane tape of this invention for 2100 seconds while the vinyl coating lasted only 300 seconds. Also, the same polyurethane coating of this invention was dropout free of over 3,000,000 cycles when tested on the revolving drum of a random access typeof memory storage device compared to only several cycles for the vinyl system.

While certain specific operative examples of this invention have been described in detail herein, it is obvious that many modifications thereof may be made without departing from the spirit and scope of the invention.

I claim:

1. A magnetic recording media which comprises a support means, and a magnetic pigment dispersed in a polyurethane binder coated on said support means where said binder comprises:

(A) a low molecular weight diol selected from the class consisting of primary and secondary aliphatic glycols containing 2 to 22 carbon atoms, polyether glycols containing 4 to 22 carbon atoms and polyester glycols having a hydroxyl number of 10 to 100 and having the following general formula -and R is an aliphatic hydrocarbon radical containing about 6 to 16 carbon atoms, and n is an integer having a value such that the molecular weight of the low molecular weight polyester diol is 216 to 3240,

(B) a high molecular weight diol having a hydroxyl number of 1 to 40 and having the following general formula where R is a benzene ring, in the ortho, meta, or para configuration, R is an aliphatic hydrocarbon radical containing about 6-16 carbon atoms, X is an integer from 7 to 30, and n is an integer having a value such that the molecular weight of the high molecular weight polyester is approximately 10,000 to 30,000,

(C) a triisocyanate selected from the class consisting of triphenyl methane triisocyanate and a prepolymer having the general formula where R is a divalent benzene radical containing an aliphatic hydrocarbon side chain of to 18 carbon atoms, 7 (D) with said low molecular weight diol, said high molecular weight diol, and said triisocyanate chemically reacted together, (E) the low molecular weight diol forming from about 10 to about 90 weight percent of said two diols, and (F) said triisocyanate being present in an amount to contribute to said binder 0.8 to 1.5 mols of active isocyanate groups per mol of active hydroxyl groups contribtued by said two diols.

2. A magnetic recording media which comprises:

(A) 6085 parts by weight of magnetic particles, and

(B) a polymeric binder for said particles containing chemically reacted together,

(1) 4l0 parts by weight of diethylene glycol adipate having a molecular weight of about 2550 and a hydroxyl number of about 44,

(2) 10-27 parts by weight of polyethylene glycol terephthalate sebacate having a molecular weight of about 20,000 and a hydroxyl number of about 2.75, and

(3) 1-3 parts by weight of an adduct of one mol of trimethylol propane and three mols of toluene-2,4 diisocyanate.

3. A magnetic recording media which comprises: (A) 60-80 parts by weight of magnetic particles, and (B) a polymeric binder for said particles containing chemically reacted together,

(1) 0.7-1.9 parts by weight of propanediol-1,5, (2) 10.0 to 26.6 parts by weight of polyethylene glycol terephthalate sebacate having a molecular weight of about 20,000 and a hydroxyl number of about 2.75, and (3) 9.3 to 11.5 parts by weight of an adduct of one mole of trimethylol propane and three mols of toluene-2,4diisocyanate. 4. A method of making a magnetic recording media which comprises:

(A) forming a mixture containing (1) a magnetic pigment,

(2) a low molecular weight diol selected from the class consisting of primary and secondary aliphatic glycols containing 2 to 22 carbon atoms, polyether glycols containing 4 to 22 carbon atoms and polyester glycols having a hydroxyl number of 10 to 100 and having the following general formula 0 HO[RO%RQJ-OR]HOH where R is the carbon chain of a glycol represented by and R is an aliphatic hydrocarbon radical containing about 6 to 16 carbon atoms, and n is an integer having a value such that the molecular weight of the low molecular weight polyester diol is 216 to 3240, i

(3) a high molecular weight diol having a hydroxyl number of 1 to 40 and having the following general formula 0 ll II I II HO[(CH;CH2);OORCO (OHzCHzhO JIRCO (CHzCHz) xlnOH where R is a benzene ring, in the ortho, meta, or para configuration, R is an aliphatic hydrocarbon radical containing about 6-16 carbon atoms, X is an integer from 7 to 30, and n is an integer having a value such that the molec ular weight of the high molecular weight polyester is approximately 10,000 to 30,000 (4) with said low molecular weight diol forming about 10 to about weight percent of the combined weights of said two diols, (B) mixing said mixture until said mixture is substantially homogeneous, (C) adding to said mixture a triisocyanate selected from the class consisting of triphenyl methane tri- 7 8 isocyanate and a prepolymer having the general for- 3,164,572 1/1965 Axelrood 260-77.5 mula 3,216,846 11/1965 Hendricx et a1. 252-6254 3,234,182 2/1966 Seeburger et a1. 26077.5X ll 3,351,573 11/1967 Skreckoski 117161X CZHSOWHZOCNRNCO 5 3,357,855 12/1967 Bisschops et a1. 117121X where R is a divalent benzene radical containing an 3,366,505 1/1963 Bi h t 1 117 121X aliphatic hydrocarbon side chain of O to 18 carbon 2,511,310 1950 Upson 2 4 5 atoms with the amount of said triisocyanate being 2,901,4 7 3 1959 c 117 143 sufiicient to provide in said mixture 0.8 to 1.5 mols 3,320 090 5 19 7 Graubart 117 13g g of active isocyanate g p p mol of active y- 10 3,411,944 11/1968 Higashi 117 121 droxyl groups in said mixture, (D) coating said mi i cture on a supporting surface, and WILLIAM D. MARTIN, Primary Examiner (E) reacting said trnsocyanate with said (11018. B. D. PIANALTO, Assistant Examiner References Cited 15 Us CL X RI UNITED STATES PATENTS 117161, 235; 252-6254; 2602.5, 75., 77.5 3,150,995 9/1964 Baur 117235UX 

